Method and system for pre-ignition control

ABSTRACT

Methods are provided for controlling an engine in response to a pre-ignition event. A pre-ignition threshold and a pre-ignition mitigating action are adjusted based on a rate of change of cylinder aircharge. As a result, pre-ignition events occurring during transient engine operating conditions are detected and addressed different from pre-ignition events occurring during steady-state engine operating conditions.

FIELD

The present description relates generally to methods and systems forcontrolling a vehicle engine to reduce the occurrence of pre-ignition.

BACKGROUND/SUMMARY

Under certain operating conditions, engines that have high compressionratios, or are boosted to increase specific output, may be prone to lowspeed pre-ignition combustion events. The early combustion due topre-ignition can cause very high in-cylinder pressures, and can resultin combustion pressure waves similar to combustion knock, but withlarger intensity. Strategies have been developed for prediction and/orearly detection of pre-ignition based on engine operating conditions.Additionally, following detection, various pre-ignition mitigating stepsmay be taken.

One example strategy for pre-ignition detection and mitigation is shownby Rollinger et al. in US2011/0139120. Therein, pre-ignition isindicated based on a knock intensity and timing, and in response to theindication of pre-ignition, a cylinder enrichment is performed. Further,in response to frequent pre-ignition occurrence, persistent pre-ignitionis inferred and mitigated with a more aggressive enrichment strategy ascompared to intermittent pre-ignition.

However, the inventors herein have identified a potential issue withsuch an approach. During transient engine operating conditions, such asduring a tip-in when boost is being phased in, rapid changes in cylinderaircharge can result in heavy knocking events. That is, the intensityand frequency of knocking may be higher for a given cylinder duringtransient conditions as compared to steady-state conditions. The heavyknocking may be incorrectly perceived as persistent pre-ignition andmitigated with too much (or too frequent) enrichment. As such, this maylead to an unintentional increase in exhaust emissions. Additionally,fuel economy may be degraded.

Thus, in one example, the above issue may be at least partly addressedby a method for an engine. In one example embodiment, the methodcomprises adjusting a timing and number of injections, in a given enginecycle, of a pre-ignition suppressing fluid injection to a cylinder basedon an indication of transient pre-ignition in the cylinder. Further, asplit ratio of the pre-ignition suppressing fluid injection may beadjusted based on the indication of transient pre-ignition.

In one example, during engine operation, an engine controller mayestimate a change in cylinder aircharge over time. In response to anindication of pre-ignition (e.g., a knock intensity) being higher than athreshold while the change in air charge over time is higher than athreshold rate, transient pre-ignition may be inferred. To mitigate thetransient pre-ignition, a pre-ignition suppressing fluid, such as wateror gasoline, may be direct injected into the pre-ignition affectedcylinder. The injection may be split into a number of injections toimprove the pre-ignition mitigating effect of the pre-ignitionsuppressing fluid. For example, as the rate of change in air chargeincreases above the threshold rate, the number of injections may beincreased, the number of injections and a duration between consecutiveinjections based on the rate of change in cylinder air charge.Additionally, a larger portion of the injection may be injected duringan intake stroke of a given engine cycle while the remaining portion isinjected during a compression stroke of the engine cycle.

In comparison, if the cylinder knock intensity is lower than theadjusted threshold, heavy knocking due to the rapid change in cylinderaircharge during the transient conditions may be inferred. Likewise,pre-ignition mitigating actions (e.g., enrichment and/or lead-limiting)may be adjusted based on the presence of transient operating conditions.Specifically, mitigating actions responsive to transient pre-ignitionmay be limited only to the affected cylinder and may be not extended toother cylinders or cylinder groups, as may be done responsive to(intermittent or persistent) steady-state pre-ignition. Optionally,engine transients may be reduced to further mitigate the transientpre-ignition.

In this way, large knocking events caused due to transient or tip-indetonation may be better distinguished from those caused due totransient pre-ignition. By reducing the false detection of pre-ignitionduring transient conditions, and adjusting the injection of apre-ignition suppressing fluid responsive to transient pre-ignition,unnecessary cylinder enrichment may be reduced while the pre-ignitionmitigating effect of the injected fluid is improved. As a result,pre-ignition mitigation, fuel economy and engine exhaust emissions maybe improved, without degrading the accuracy of pre-ignition detection.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example engine system.

FIG. 2 shows an example combustion chamber.

FIG. 3 shows a high level flow chart for adjusting a cylinderpre-ignition mitigating action, and a pre-ignition threshold based ontransient or steady-state engine operating conditions.

FIG. 4 shows a high level flow chart for adjusting a cylinderpre-ignition mitigating action in response to transient pre-ignition,intermittent pre-ignition or persistent pre-ignition.

FIG. 5 shows example cylinder pre-ignition events during steady-stateand transient engine operating conditions, according to the presentdisclosure.

FIG. 6 shows a high level flow chart for adjusting a cylinderpre-ignition suppressing fluid injection in response to transientpre-ignition, intermittent pre-ignition or persistent pre-ignition.

FIGS. 7-8 show example cylinder pre-ignition suppressing fluidinjections, according to the present disclosure

DETAILED DESCRIPTION

The following description relates to systems and methods for adjustingthe detection and mitigation of pre-ignition in an engine, such as theengine system of FIGS. 1-2, based on a rate of change of a parameterindicative of cylinder aircharge. In this way, heavy knocking duringtransient engine operating conditions may be better differentiated fromactual pre-ignition events. An engine controller may be configured toperform control routines, such as the example routines of FIGS. 3-4, toadjust a cylinder pre-ignition threshold as well as a pre-ignitionmitigating action (such as, an enrichment and/or a load-limiting) basedon the estimated rate of change of cylinder aircharge. An examplecylinder operation is illustrated herein with reference to FIG. 5. Theengine controller may be further configured to adjust the injection(e.g., timing, number of injections, split ratio, etc.) of apre-ignition suppressing fluid in response to an indication ofpre-ignition based on whether the pre-ignition is transient,intermittent, or persistent in nature. Example cylinder injections areillustrated herein with reference to FIGS. 7-8. By improving thedetection of transient pre-ignition, wasteful fuel enrichment due tointense knocking during transient engine operating conditions may bereduced. By adjusting the pre-ignition mitigating action, such as apre-ignition suppressing fluid injection, based on whether thepre-ignition is during transient or steady-state conditions, thepre-ignition suppressing action of the injected fluid can be improvedand further pre-ignition can be reduced.

FIG. 1 shows a schematic depiction of a vehicle system 6 including anengine system 8. The engine system 8 may include an engine 10 having aplurality of cylinders 30. Engine 10 includes an engine intake 23 and anengine exhaust 25. Engine intake 23 includes a throttle 62 fluidlycoupled to the engine intake manifold 44 via an intake passage 42. Theengine exhaust 25 includes an exhaust manifold 48 eventually leading toan exhaust passage 35 that routes exhaust gas to the atmosphere.Throttle 62 may be located in intake passage 42 downstream of a boostingdevice, such as turbocharger 50, or a supercharger, and upstream of anafter-cooler (not shown). As such, the after-cooler may be configured toreduce the temperature of the intake air compressed by the boostingdevice. Turbocharger 50 may include a compressor 52, arranged betweenintake passage 42 and intake manifold 44. Compressor 52 may be at leastpartially powered by exhaust turbine 54, arranged between exhaustmanifold 48 and exhaust passage 35, via turbine shaft 56.

Engine exhaust 25 may include one or more emission control devices 70,which may be mounted in a close-coupled position in the exhaust. One ormore emission control devices may include a three-way catalyst, lean NOxfilter, SCR catalyst, PM filter, etc.

Engine system 8 may further include one (as depicted) or more knocksensors 90 distributed along engine block 11. When included, theplurality of knock sensors may be distributed symmetrically orasymmetrically along the engine block. Knock sensor 90 may be anaccelerometer, or an ionization sensor.

In one example, an engine controller may be configured to detect anddifferentiate abnormal combustion events due to cylinder knocking fromthose indicative of cylinder pre-ignition based on the output (e.g.,signal timing, amplitude, intensity, frequency, etc.) of the one or moreknock sensors 90. In one example, a cylinder pre-ignition event may bedetermined based on a cylinder knock signal estimated in a first,earlier window being larger than a first, higher threshold, while acylinder knock event may be determined based on a cylinder knock signalestimated in a second, later window being larger than a second, lowerthreshold. In one example, the windows in which the knock signals areestimated may be crank angle windows.

In another example, as elaborated in FIG. 3, the engine controller maybe configured to detect and differentiate abnormal combustion events dueto cylinder knocking from those indicative of cylinder pre-ignitionduring transient or steady-state engine operating conditions based onthe output (e.g., signal timing, amplitude, intensity, frequency, etc.)of the one or more knock sensors as well as a rate of change of aparameter indicative of a cylinder aircharge. For example, thecontroller may infer transient engine operating conditions based on therate of change of a manifold pressure (MAP), a manifold air flow (MAF),a throttle position or throttle angle, an accelerator pedal or brakepedal position, etc., being higher than a threshold rate. Inanticipation of more intense and/or more frequent knocking events,rather than pre-ignition events, during the transient operatingconditions (at least due to the rapid change in air mass), thecontroller may use adjusted knock and pre-ignition thresholds that arehigher than the unadjusted knock and pre-ignition thresholds used fordetecting knock and pre-ignition during steady-state engine operatingconditions (when the rate of change in air mass is substantially lower).

Pre-ignition may be determined based on still other indications ofpre-ignition. For example, pre-ignition may be determined based on anin-cylinder pressure (as estimated by a pressure sensor coupled to thecylinder), the output of one or more ionization sensors, and/or acrankshaft acceleration. Based on the rate of change of the parameterindicative of cylinder aircharge at the time when the indication ofpre-ignition is received, transient pre-ignition or steady-statepre-ignition may be determined. Likewise, based at least on a cylinderpre-ignition count (or a number of consecutive pre-ignition events overa specified time interval), intermittent or persistent steady-statepre-ignition may be determined and differentiated.

Mitigating actions taken by the engine controller to address knock mayalso differ from those taken by the controller to address pre-ignition.For example, knock may be addressed using ignition spark timingadjustments (e.g., spark retard) and EGR, while pre-ignition may beaddressed using load-limiting, fuel enrichment, fuel enleanment, directinjection of a knock-suppressing fluid (such as water), or combinationsthereof. In the same way mitigating actions taken by the controller toaddress pre-ignition during the transient conditions may differ fromthose taken during the steady-state conditions. For example, transientpre-ignition may be addressed by enriching only the affected cylinderwhile during steady-state pre-ignition, one or more other cylinders mayalso be enriched in addition to the affected cylinder, as elaborated inFIG. 4. Further still, the enrichment may be adjusted based on whetherthe steady-state pre-ignition is intermittent or persistent. Forexample, a more aggressive mitigation approach may be used in responseto persistent pre-ignition with the enrichment of a pre-ignitionaffected cylinder and cylinder group as well as the unaffected cylindergroup. Likewise, an engine load of the affected cylinder and cylindergroup may be limited during intermittent pre-ignition while the engineload of all the cylinder groups (pre-ignition affected and unaffected)may be limited during persistent pre-ignition. In comparison, duringtransient pre-ignition, the engine load may be maintained and no loadlimiting may be used.

In still further embodiments, as elaborated in FIG. 6, theknock-suppressing fluid that is injected responsive to the pre-ignition,as well as the injection of the fluid (e.g., the timing of theinjection, the number of injections in a given engine cycle, theamount/proportion of the fluid injected during an intake stroke relativeto a compression stroke, the amount/proportion of fluid direct injectedinto the cylinder relative to an amount port injected into the cylinder,etc.) may be adjusted based on the nature of the pre-ignition. Forexample, as illustrated with reference to FIGS. 7-8, a larger number ofinjections with a shorter duration between consecutive injections may beused to mitigate persistent pre-ignition while a smaller number ofinjections with a longer duration between consecutive injections may beused to mitigate transient pre-ignition. Likewise, a larger proportionof the injected fluid may be injected earlier in an engine cycle (e.g.,in an intake stroke) to mitigate transient pre-ignition while a largerproportion of the injected fluid may be injected later in an enginecycle (e.g., in a compression stroke) to mitigate persistentpre-ignition.

The vehicle system 6 may further include control system 14. Controlsystem 14 is shown receiving information from a plurality of sensors 16(various examples of which are described herein) and sending controlsignals to a plurality of actuators 81 (various examples of which aredescribed herein). As one example, sensors 16 may include exhaust gassensor 126 (located in exhaust manifold 48), knock sensor(s) 90,temperature sensor 127, and pressure sensor 129 (located downstream ofemission control device 70). Other sensors such as pressure,temperature, air/fuel ratio, composition, ionization sensors, etc., maybe coupled to various locations in the vehicle system 6, as discussed inmore detail herein. As another example, the actuators may include fuelinjectors 66, and throttle 62. The control system 14 may include acontroller 12. The controller may receive input data from the varioussensors, process the input data, and trigger the actuators in responseto the processed input data based on instruction or code programmedtherein corresponding to one or more routines. Example control routinesare described herein with reference to FIGS. 3-4 and 6.

FIG. 2 depicts an example embodiment of a combustion chamber or cylinderof internal combustion engine 10 (of FIG. 1). Engine 10 may receivecontrol parameters from a control system including controller 12 andinput from a vehicle operator 130 via an input device 132. In thisexample, input device 132 includes an accelerator pedal and a pedalposition sensor 134 for generating a proportional pedal position signalPP. Cylinder (herein also “combustion chamber”) 30 of engine 10 mayinclude combustion chamber walls 136 with piston 138 positioned therein.Piston 138 may be coupled to crankshaft 140 so that reciprocating motionof the piston is translated into rotational motion of the crankshaft.Crankshaft 140 may be coupled to at least one drive wheel of thepassenger vehicle via a transmission system. Further, a starter motormay be coupled to crankshaft 140 via a flywheel to enable a startingoperation of engine 10.

Cylinder 30 can receive intake air via a series of intake air passages142, 144, and 146. Intake air passage 146 can communicate with othercylinders of engine 10 in addition to cylinder 30. In some embodiments,one or more of the intake passages may include a boosting device such asa turbocharger or a supercharger. For example, FIG. 2 shows engine 10configured with a turbocharger including a compressor 174 arrangedbetween intake passages 142 and 144, and an exhaust turbine 176 arrangedalong exhaust passage 148. Compressor 174 may be at least partiallypowered by exhaust turbine 176 via a shaft 180 where the boosting deviceis configured as a turbocharger. However, in other examples, such aswhere engine 10 is provided with a supercharger, exhaust turbine 176 maybe optionally omitted, where compressor 174 may be powered by mechanicalinput from a motor or the engine. A throttle 20 including a throttleplate 164 may be provided along an intake passage of the engine forvarying the flow rate and/or pressure of intake air provided to theengine cylinders. For example, throttle 20 may be disposed downstream ofcompressor 174 as shown in FIG. 2, or alternatively may be providedupstream of compressor 174.

Exhaust passage 148 can receive exhaust gases from other cylinders ofengine 10 in addition to cylinder 30. Exhaust gas sensor 128 is showncoupled to exhaust passage 148 upstream of emission control device 178.Sensor 128 may be selected from among various suitable sensors forproviding an indication of exhaust gas air/fuel ratio such as a linearoxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), atwo-state oxygen sensor or EGO (as depicted), a HEGO (heated EGO), aNOx, HC, or CO sensor, for example. Emission control device 178 may be athree way catalyst (TWC), NOx trap, various other emission controldevices, or combinations thereof.

Exhaust temperature may be estimated by one or more temperature sensors(not shown) located in exhaust passage 148. Alternatively, exhausttemperature may be inferred based on engine operating conditions such asspeed, load, air-fuel ratio (AFR), spark retard, etc. Further, exhausttemperature may be computed by one or more exhaust gas sensors 128. Itmay be appreciated that the exhaust gas temperature may alternatively beestimated by any combination of temperature estimation methods listedherein.

Each cylinder of engine 10 may include one or more intake valves and oneor more exhaust valves. For example, cylinder 30 is shown including atleast one intake poppet valve 150 and at least one exhaust poppet valve156 located at an upper region of cylinder 30. In some embodiments, eachcylinder of engine 10, including cylinder 30, may include at least twointake poppet valves and at least two exhaust poppet valves located atan upper region of the cylinder.

Intake valve 150 may be controlled by controller 12 by cam actuation viacam actuation system 151. Similarly, exhaust valve 156 may be controlledby controller 12 via cam actuation system 153. Cam actuation systems 151and 153 may each include one or more cams and may utilize one or more ofcam profile switching (CPS), variable cam timing (VCT), variable valvetiming (VVT) and/or variable valve lift (VVL) systems that may beoperated by controller 12 to vary valve operation. The position ofintake valve 150 and exhaust valve 156 may be determined by valveposition sensors 155 and 157, respectively. In alternative embodiments,the intake and/or exhaust valve may be controlled by electric valveactuation. For example, cylinder 30 may alternatively include an intakevalve controlled via electric valve actuation and an exhaust valvecontrolled via cam actuation including CPS and/or VCT systems. In stillother embodiments, the intake and exhaust valves may be controlled by acommon valve actuator or actuation system, or a variable valve timingactuator or actuation system.

Cylinder 30 can have a compression ratio, which is the ratio of volumeswhen piston 138 is at bottom center to top center. Conventionally, thecompression ratio is in the range of 9:1 to 10:1. However, in someexamples where different fuels are used, the compression ratio may beincreased. This may happen, for example, when higher octane fuels orfuels with higher latent enthalpy of vaporization are used. Thecompression ratio may also be increased if direct injection is used dueto its effect on engine knock.

In some embodiments, each cylinder of engine 10 may include a spark plug192 for initiating combustion. Ignition system 190 can provide anignition spark to combustion chamber 30 via spark plug 192 in responseto spark advance signal SA from controller 12, under select operatingmodes. However, in some embodiments, spark plug 192 may be omitted, suchas where engine 10 may initiate combustion by auto-ignition or byinjection of fuel as may be the case with some diesel engines.

In some embodiments, each cylinder of engine 10 may be configured withone or more injectors for providing a knock or pre-ignition suppressingfluid thereto. In some embodiments, the fluid may be a fuel, wherein theinjector is also referred to as a fuel injector. As a non-limitingexample, cylinder 30 is shown including one fuel injector 166. Fuelinjector 166 is shown coupled directly to cylinder 30 for injecting fueldirectly therein in proportion to the pulse width of signal FPW receivedfrom controller 12 via electronic driver 168. In this manner, fuelinjector 166 provides what is known as direct injection (hereafter alsoreferred to as “DI”) of fuel into combustion cylinder 30. While FIG. 2shows injector 166 as a side injector, it may also be located overheadof the piston, such as near the position of spark plug 192. Such aposition may improve mixing and combustion when operating the enginewith an alcohol-based fuel due to the lower volatility of somealcohol-based fuels. Alternatively, the injector may be located overheadand near the intake valve to improve mixing.

Fuel may be delivered to fuel injector 166 from a high pressure fuelsystem 80 including fuel tanks, fuel pumps, and a fuel rail.Alternatively, fuel may be delivered by a single stage fuel pump atlower pressure, in which case the timing of the direct fuel injectionmay be more limited during the compression stroke than if a highpressure fuel system is used. Further, while not shown, the fuel tanksmay have a pressure transducer providing a signal to controller 12. Itwill be appreciated that, in an alternate embodiment, injector 166 maybe a port injector providing fuel into the intake port upstream ofcylinder 30.

It will also be appreciated that while in one embodiment, the engine maybe operated by injecting a variable fuel blend or knock/pre-ignitionsuppressing fluid via a single direct injector; in alternateembodiments, the engine may be operated by using two injectors (a directinjector 166 and a port injector) and varying a relative amount ofinjection from each injector.

Fuel may be delivered by the injector to the cylinder during a singleengine cycle of the cylinder. Further, the distribution and/or relativeamount of fuel or knock/pre-ignition suppressing fluid delivered fromthe injector may vary with operating conditions (in particular, the rateof change of a cylinder aircharge), as well as a nature of thepre-ignition (such as, transient or intermittent or persistentpre-ignition). Furthermore, for a single combustion event, multipleinjections of the delivered fuel may be performed per cycle. Themultiple injections may be performed during the compression stroke,intake stroke, or any appropriate combination thereof.

As described above, FIG. 2 shows only one cylinder of a multi-cylinderengine. As such each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector(s), spark plug, etc.

Fuel tanks in fuel system 80 may hold fuel or knock/pre-ignitionsuppressing fluids with different qualities, such as differentcompositions. These differences may include different alcohol content,different water content, different octane, different heat ofvaporizations, different fuel blends, and/or combinations thereof etc.In one example, fuels or knock/pre-ignition suppressing fluids withdifferent alcohol contents could include one fuel being gasoline and theother being ethanol or methanol. In another example, the engine may usegasoline as a first substance and an alcohol containing fuel blend suchas E85 (which is approximately 85% ethanol and 15% gasoline) or M85(which is approximately 85% methanol and 15% gasoline) as a secondsubstance. Other alcohol containing fuels could be a mixture of alcoholand water, a mixture of alcohol, water and gasoline etc. In stillanother example, both fuels may be alcohol blends wherein the first fuelmay be a gasoline alcohol blend with a lower ratio of alcohol than agasoline alcohol blend of a second fuel with a greater ratio of alcohol,such as E10 (which is approximately 10% ethanol) as a first fuel and E85(which is approximately 85% ethanol) as a second fuel. In yet anotherexample, one of the fluids may include water while the other fluid isgasoline or an alcohol blend. Additionally, the first and second fuelsmay also differ in other fuel qualities such as a difference intemperature, viscosity, octane number, latent enthalpy of vaporizationetc. Still other pre-ignition suppressing fluids may include water,methanol, washer fluid (which is a mixture of approximately 60% waterand 40% methanol), etc.

Moreover, fuel characteristics of the fuel or pre-ignition suppressingfluid stored in the fuel tank may vary frequently. In one example, adriver may refill the fuel tank with E85 one day, and E10 the next, andE50 the next. The day to day variations in tank refilling can thusresult in frequently varying fuel compositions, thereby affecting thefuel composition delivered by injector 166.

Controller 12 is shown in FIG. 2 as a microcomputer, includingmicroprocessor unit 106, input/output ports 108, an electronic storagemedium for executable programs and calibration values shown as read onlymemory chip 110 in this particular example, random access memory 112,keep alive memory 114, and a data bus. Controller 12 may receive varioussignals from sensors coupled to engine 10, in addition to those signalspreviously discussed, including measurement of inducted mass air flow(MAF) from mass air flow sensor 122; engine coolant temperature (ECT)from temperature sensor 116 coupled to cooling sleeve 118; a profileignition pickup signal (PIP) from Hall effect sensor 120 (or other type)coupled to crankshaft 140; throttle position (TP) from a throttleposition sensor; absolute manifold pressure signal (MAP) from sensor124, cylinder AFR from EGO sensor 128, and abnormal combustion from aknock sensor and a crankshaft acceleration sensor. Engine speed signal,RPM, may be generated by controller 12 from signal PIP. Manifoldpressure signal MAP from a manifold pressure sensor may be used toprovide an indication of vacuum, or pressure, in the intake manifold.

Storage medium read-only memory 110 can be programmed with computerreadable data representing instructions executable by processor 106 forperforming the methods described below as well as other variants thatare anticipated but not specifically listed.

Now turning to FIG. 3, an example routine 300 is shown for detectingsteady-state or transient pre-ignition and adjusting engine operationsbased on the detection of pre-ignition.

At 302, engine operating conditions may be estimated and/or measured.These may include, for example, engine speed, operator torque demand,boost, exhaust temperature, etc. At 304, a rate of change of a parameterindicative of cylinder aircharge may be determined. That is, aderivative of aircharge with respect to time may be determined. In oneexample, the parameter may include one or more of manifold air pressure(MAP), manifold air flow (MAF), actual cylinder aircharge, a throttleposition, a pedal (e.g., accelerator pedal) position, etc. At 306, basedon the determined rate of change of the cylinder aircharge, it may bedetermined whether transient engine operating conditions are prevalent.Specifically, if the rate of change of cylinder aircharge is greaterthan a threshold rate, transient engine operating conditions may bedetermined. In comparison, if the rate of change of cylinder airchargeis lower than the threshold rate, steady-state engine operatingconditions may be determined.

Based on whether the engine operating conditions are transient orsteady-state, a threshold for detecting pre-ignition, as well as athreshold for detecting knock may be adjusted. Specifically, theunadjusted thresholds may be used for detecting and differentiatingknock and pre-ignition under steady-state conditions while the adjustedthresholds may be used for detecting and differentiating knock andpre-ignition under transient conditions. As such, a cylinder may be moreprone to intense and frequent knocking during transient operatingconditions (such as during a tip-in) as compared to steady-stateoperating conditions due to the rapid change in air mass and flowexperienced in the cylinder during the transient conditions. Thisintense knocking, when compared related to the unadjusted thresholds,may be erroneously inferred as a pre-ignition event and addressed withcylinder enrichment. Thus, to better distinguish heavy knocking from anactual pre-ignition event during transient conditions, adjustedthresholds that are higher than their unadjusted counterparts may beused.

Specifically, if transient engine operating conditions are confirmed, at308, the routine includes adjusting a cylinder pre-ignition thresholdbased on the estimated rate of change of cylinder aircharge. Theadjustment may include, for example, increasing the pre-ignitionthreshold as the estimated rate of change of the parameter indicative ofcylinder aircharge increases above the threshold rate. The adjustedthreshold may be an absolute threshold that is stored in the controllerin a look-up table and accessed based on the rate of change of thecylinder aircharge. Alternatively, the threshold may be a relativethreshold based on the unadjusted steady-state threshold, for example,as a function of the unadjusted threshold and the rate of change ofcylinder aircharge. For example, the controller may use a map that has arate of change of cylinder aircharge with respect to time as an input.The input may be processed through a 2-D function that is a thresholdmultiplier against the steady-state threshold to provide an adjustedthreshold as the output. For example, when the rate of change over timeis 0 (that is, at steady-state engine operating conditions), themultiplier would be 1.0, and at higher rates of change (that is attransient conditions), the multiplier would be greater than 1.0. Theknock threshold may also be similarly adjusted. Thus, by increasing thethreshold for comparing knock and pre-ignition based on the transientair charge value during a transient change in air mass, heavy knockingexperienced during transient conditions may be better distinguished fromtransient pre-ignition, and appropriately addressed.

At 310, it may be determined if the indication of pre-ignition in thecylinder is higher than the unadjusted (pre-ignition) threshold. In oneexample, the indication of pre-ignition may be based on a knockintensity, as estimated by a knock sensor such as knock sensor 90 ofFIG. 1, as estimated at a predetermined crank angle degree/timing, or ina predetermined crank angle degree/timing window. In another example,the indication of pre-ignition may be based on a crankshaft acceleration(e.g., in deg/sec²). Still other parameters may be used, such asionization values and in-cylinder pressures. If the indication is nothigher than the unadjusted threshold, then the routine may end as noabnormal combustion event is inferred. If yes, then it may be furtherdetermined if the indication of pre-ignition in the cylinder is higherthan the adjusted (pre-ignition) threshold. If the indication ofpre-ignition is higher than the unadjusted threshold but lower than theadjusted threshold, then it may be determined that the abnormalcombustion event is a cylinder knocking event and no transientpre-ignition may be determined. Accordingly, no pre-ignition mitigatingaction may be performed. Rather, a knock mitigating action may beperformed. For example, knock may be addressed using an amount of sparkretard and/or an amount of EGR. It will be appreciated that in analternate embodiment, cylinder knocking may be inferred based on theknock intensity being higher than an adjusted knock threshold. If theindication of pre-ignition is higher than the unadjusted pre-ignitionthreshold and the adjusted pre-ignition threshold, then at 316, atransient pre-ignition event may be inferred and indicated. In responseto the cylinder pre-ignition event and the determination of transientpre-ignition, a transient pre-ignition mitigating action may beperformed at 318.

If transient engine operating conditions are not confirmed at 306, thenat 320, steady-state conditions may be confirmed. Specifically, if therate of change of cylinder aircharge is lower than the threshold rate,steady-state engine operating conditions may be determined. In oneexample, a steady-state operating condition may be determined when thereis no change in the rate (that is, when the derivative of cylinderaircharge over time is 18 1.0). If steady-state conditions areconfirmed, then at 322, the pre-ignition and knock thresholds may not beadjusted and at 324, it may be determined if the indication ofpre-ignition in the cylinder is higher than the unadjusted(pre-ignition) threshold. In one example, it may be determined if aknock intensity in the cylinder is higher than the unadjusted threshold.If the indication of pre-ignition is not higher than the unadjustedpre-ignition threshold, then no pre-ignition combustion event may beinferred. In one example, a cylinder knocking event may be determinedwhen the knock intensity during steady-state conditions is lower thanthe unadjusted pre-ignition threshold. In an alternate example, acylinder knocking event may be further determined when the knockintensity during steady-state conditions is higher than an unadjustedknock threshold (but lower than the unadjusted pre-ignition threshold).

If the indication of pre-ignition in the cylinder is higher than theunadjusted threshold, then at 326, it may be determined that theabnormal combustion event is due to a steady-state pre-ignition event.At 328, the nature of the steady-state pre-ignition may be furtherdetermined based on, for example, a cylinder pre-ignition count, acylinder pre-ignition history, pre-ignition frequency, etc. For example,it may be determined whether the steady-state pre-ignition isintermittent or persistent based on a number of consecutive pre-ignitionevents. Thus, while the engine is in the steady-state, intermittentpre-ignition may be inferred if the number of consecutive pre-ignitionevents in the cylinder is lower than a threshold number while persistentpre-ignition may be inferred if the number of consecutive pre-ignitionevents in the cylinder is higher than a threshold number. In alternateembodiments, a cylinder pre-ignition count may be updated (e.g.,increased) after every pre-ignition event and intermittent versuspersistent pre-ignition may be determined based on the updatedpre-ignition count. In response to the cylinder pre-ignition event andthe determination of steady-state (intermittent or persistent)pre-ignition, a steady-state pre-ignition mitigating action may beperformed at 330.

As further elaborated in FIG. 4, the cylinder pre-ignition mitigatingaction performed may also be adjusted based on the rate of change of theparameter indicative of cylinder aircharge. Specifically, the cylinderpre-ignition mitigating action may be adjusted based on whether thepre-ignition is transient pre-ignition or steady-state pre-ignition, andfurther based on whether the steady-state pre-ignition is intermittentpre-ignition or persistent pre-ignition. For example, at 318, when therate of change of cylinder aircharge is higher than the threshold rate(that is, in response to transient pre-ignition), the pre-ignitionmitigating action may include enriching only the cylinder affected bythe pre-ignition event. In comparison, at 330, when the rate of changeof cylinder aircharge is lower than the threshold rate (that is, inresponse to steady-state pre-ignition), the pre-ignition mitigatingaction may include enriching one or more cylinders other than thecylinder affected by the pre-ignition event. Further, where the engineincludes a plurality of cylinders arranged in different cylinder groups,in response to intermittent pre-ignition, the affected cylinder and oneor more cylinders on the pre-ignition affected cylinder group may beenriched. In comparison, in response to persistent pre-ignition, theaffected cylinder and cylinder group, as well as a pre-ignitionunaffected cylinder group may be enriched. In this way, by adjusting acylinder pre-ignition threshold as well as a pre-ignition mitigatingaction based on the presence of transient engine operating conditions,erroneous pre-ignition detection and unnecessary cylinder enrichment canbe reduced.

Now turning to FIG. 4, an example routine 400 is described for adjustinga pre-ignition mitigating action based on a rate of change of a cylinderaircharge. Specifically, different pre-ignition mitigating actions maybe performed in response to transient pre-ignition as compared to(intermittent or persistent) steady-state pre-ignition in an engineincluding a plurality of cylinders arranged on a first and secondcylinder group.

At 402, it may be determined if transient pre-ignition is present in afirst cylinder included in the first cylinder group. In one example,transient pre-ignition includes a number of consecutive pre-ignitionevents in the first cylinder being higher than a threshold while theengine is in a transient state (where the rate of change in cylinderaircharge is higher). Upon confirmation of transient pre-ignition in thefirst cylinder, the routine includes, at 404, adjusting the enrichmentprofile of only the first cylinder such that only the first cylinder isenriched. As such, the enrichment in response to transient pre-ignitionmay be of a shorter duration (e.g., a first shorter duration) while thedegree of enrichment in response to the cylinder transient pre-ignitionevent may be adjusted based on the indication of transient pre-ignition(such as a knock intensity or a knock/pre-ignition sensor output). Theduration (e.g., the first shorter duration) may be based on the rate ofchange of cylinder aircharge during the transient condition. Forexample, as the rate of change of cylinder aircharge increases above thethreshold rate, the duration of enrichment responsive to the transientpre-ignition may be increased. In some embodiments, a degree of theenrichment may also be increased as the rate of change of cylinderaircharge increases above the threshold.

At 406, while the pre-ignition affected cylinder is enriched, an engineload may be maintained in response to the transient pre-ignition. Thatis, no load-limiting may be performed in the first cylinder. Optionally,at 408, one or more engine operating parameters may be adjusted toreduce transient aircharge conditions. For example, where the engine isa boosted engine, in response to transient pre-ignition, a rate ofincrease in boost may be reduced, the reduction based on the rate ofchange of cylinder aircharge. In another example, in response totransient pre-ignition, an intake throttle responsiveness may bereduced, the reduction based on the rate of change of cylinderaircharge. In one example, the throttle may be moved with a gain factor,or adaptive term, that is based on (e.g., a function of) the rate ofchange of cylinder aircharge, the pre-ignition rate (e.g., pre-ignitiontransient rate, pre-ignition steady-state rate), or combinationsthereof. By adjusting the throttle responsiveness as a function of therate, the responsiveness of the throttle may be reduced to allowpre-ignition inducing transients to be curbed without making thethrottle non-responsive to the operator. In this way, by reducing theoccurrence of aircharge transients, the likelihood of further transientpre-ignition can be reduced.

If transient pre-ignition is not confirmed at 402, then at 410,intermittent pre-ignition may be confirmed. In one example, intermittentpre-ignition may include a number of consecutive pre-ignition events ina first cylinder being lower than a threshold while the engine is in asteady-state (where the rate of change in cylinder aircharge is lower).If confirmed, then at 412, in response to intermittent pre-ignition inthe first cylinder of the first cylinder group, the routine includesenriching one or more cylinders of the first cylinder group. In oneexample, only the affected cylinder may be enriched while in analternate example, all the cylinders of the first cylinder group may beenriched. However, in response to intermittent pre-ignition in the firstcylinder of the first cylinder group, the second cylinder group may notbe enriched. That is, only the affected cylinder and one or more othercylinders in the affected cylinder group may be enriched, but theunaffected cylinder group may not be enriched. As such, the enrichmentin response to intermittent pre-ignition may be of a longer duration(e.g., a second, longer duration) than the enrichment in response totransient pre-ignition while the degree of enrichment in response to thecylinder intermittent pre-ignition event may be adjusted based on theindication of intermittent pre-ignition (such as a knock intensity or aknock/pre-ignition sensor output). In an alternate example, the degreeof enrichment in response to intermittent pre-ignition may also behigher than the degree of enrichment in response to transientpre-ignition. Further, the enrichment of the one or more cylinders ofthe first cylinder group may be the same as the first cylinder.Alternatively, the first affected cylinder may be enriched more than theother cylinders of the affected cylinder group.

At 414, in response to intermittent pre-ignition in the first cylinder,in addition to the enrichment, an engine load of the first cylindergroup may be limited while the engine load of the second cylinder groupis maintained. That is, load-limiting may be performed only in the firstcylinder group affected by the pre-ignition and no load-limiting may beperformed in the second cylinder group that in unaffected by thepre-ignition.

If intermittent pre-ignition is not confirmed at 410, then at 416,persistent pre-ignition may be confirmed. In one example, persistentpre-ignition may include a number of consecutive pre-ignition events inthe first cylinder being higher than the threshold while the engine isin the steady-state. If confirmed, then at 418, in response topersistent pre-ignition in the first cylinder of the first cylindergroup, the routine includes enriching one or more cylinders of each ofthe first and second cylinder group. Specifically, in response topersistent pre-ignition in the first cylinder of the first cylindergroup, the second cylinder group may also be enriched. Herein, byenriching the affected cylinder, one or more other cylinders in theaffected cylinder group, as well as one or more cylinders in theunaffected cylinder group, the likelihood of further pre-ignition may bereduced. As such, the enrichment in response to persistent pre-ignitionmay be of a longer duration than the enrichment in response to transientpre-ignition or intermittent pre-ignition (e.g., a third duration longerthan each of the first and second durations) while the degree ofenrichment in response to the cylinder persistent pre-ignition event maybe adjusted based on the indication of persistent pre-ignition (such asa knock intensity or a knock/pre-ignition sensor output). In analternate example, the degree of enrichment in response to persistentpre-ignition may also be higher than the degree of enrichment inresponse to both transient and intermittent pre-ignition. Further, theenrichment of the one or more cylinders of the second cylinder group maybe the same as the first cylinder and first cylinder group.Alternatively, the first affected cylinder and first cylinder group maybe enriched more than the cylinders of the unaffected second cylindergroup.

At 420, in response to the persistent pre-ignition in the firstcylinder, in addition to the enrichment, an engine load of each of thefirst and second cylinder groups may be limited. That is, load-limitingmay be extended to the pre-ignition unaffected second cylinder group inresponse to intermittent pre-ignition in the affected cylinder of thefirst cylinder group. As used herein, load-limiting may include reducingan amount of boost, adjusting a throttle position to reduce an amount ofintake air, and/or adjusting a cam timing of the cylinder group toadjust an amount of aircharge delivered to the cylinders of thatcylinder group.

It will be appreciated that while the routines of FIGS. 3-4 suggestenriching a cylinder/cylinder group(s) immediately in response to a(transient, steady-state, intermittent or persistent) pre-ignitioncombustion event, in alternate embodiments, the pre-ignition count orpre-ignition indication (e.g., knock intensity) may be integrated over afew cycles and when the integrated count or intensity is higher than athreshold, the appropriate enrichment may be initiated. The enrichmentmay be adjusted to be a function of the integrated count or intensity,at least up to a predetermined saturation point, after which theenrichment may be clipped. By adjusting the enrichment based on theintegrated intensity, the amount of enrichment and fuel required may bereduced, providing further fuel economy benefits.

Now turning to FIG. 5, map 500 illustrates an example of pre-ignitiondetection and mitigation during steady-state and transient engineoperating conditions. Based on a rate of change of cylinder aircharge, apre-ignition threshold and a pre-ignition mitigating action may beadjusted so that heavy knocking during transient conditions may bedifferentiated from transient pre-ignition, while also differentiatingpre-ignition during transient conditions from (intermittent orpersistent) pre-ignition during steady-state conditions.

Graph 502 depicts the output of a sensor that provides an indication ofcylinder pre-ignition. In one example, the sensor is a knock sensor andthe indication of cylinder pre-ignition includes a knock intensity.Graph 504 depicts a rate of change of a parameter indicative of acylinder aircharge (dAir/dt). As shown, between t0 and t1, a firststeady-state engine operating condition is shown wherein the rate ofchange in the cylinder aircharge is lower than a threshold. Between t1and t2, a second, transient engine operating condition is shown whereinthe rate of change in the cylinder aircharge is higher than thethreshold. As such, the transient engine operating condition may be atransient condition between the first steady-state engine operatingcondition (at t0 to t1) and a second steady-state operating condition(after t2).

During the first steady-state engine operating condition (between t0 andt1), a cylinder knock intensity output by a knock sensor may be comparedto a set of unadjusted thresholds 506, 508, wherein 506 represents anunadjusted knock threshold and 508 represents an unadjusted pre-ignitionthreshold. As such, the knock threshold may be lower than thepre-ignition threshold. During the first steady-state condition, whenthe sensor output is above the unadjusted knock threshold 506, but belowthe unadjusted pre-ignition threshold, a steady-state knock event (K)may be indicated. In comparison, when the sensor output is above thefirst unadjusted pre-ignition threshold 508, a steady-state cylinderpre-ignition event (P) may be indicated. In the depicted example, thenumber of consecutive pre-ignition events during the steady-stateoperating condition may be lower than a threshold number and thepre-ignition event (P) may be determined to be intermittent steady-statepre-ignition. In an alternate example, the number of consecutivepre-ignition events during the steady-state operating condition may behigher than the threshold number wherein the pre-ignition event (P) maybe determined to be persistent steady-state pre-ignition.

During the second transient engine operating condition (between t1 andt2), in response to the rate of change of cylinder aircharge beinghigher than a threshold, at least the pre-ignition threshold may beadjusted to a second threshold 510. As such, the adjusted pre-ignitionthreshold 510 may be higher than the first unadjusted pre-ignitionthreshold 508 and may be based on, for example, the first pre-ignitionthreshold 508 and a rate of change in the cylinder aircharge (e.g., theslope of graph 504 between t1 and t2). In some embodiments, in additionto the pre-ignition threshold, the knock threshold may also be adjusted.For example, the adjusted knock threshold 509 may be higher than thefirst unadjusted knock threshold 506 and may be based on, for example,the first knock threshold 506 and a rate of change in the cylinderaircharge. While the depicted example illustrates the adjusted knockthreshold 509 as being lower than the unadjusted pre-ignition threshold508, in alternate embodiments, the adjusted knock threshold 509 may behigher than the unadjusted pre-ignition threshold 508. However, theadjusted knock threshold 509 is lower than the adjusted pre-ignitionthreshold 510.

As illustrated, during the second transient operating condition, acylinder knock intensity output by the knock sensor is compared to theset of adjusted thresholds 509, 510 to provide an indication of knock orpre-ignition. Herein, during the second transient condition, when thesensor output is above the adjusted knock threshold 509 but below theadjusted pre-ignition threshold 510, a transient knock event (K) may beindicated. That is, during transient conditions, no cylinderpre-ignition event is indicated even when the sensor output is above thefirst unadjusted pre-ignition threshold 508. Rather, when the sensoroutput is above the second, higher adjusted pre-ignition threshold 510,a transient cylinder pre-ignition event (P) is indicated. In this way,by adjusting a pre-ignition threshold for a cylinder based on a rate ofchange of aircharge of the cylinder, and by further indicating transientpre-ignition in the cylinder in response to an indication ofpre-ignition in the cylinder being higher than the adjusted threshold,the detection of transient pre-ignition can be improved.

The mitigating actions can also be appropriately adjusted based on thenature of the detected abnormal combustion event. For example, knock maybe mitigated using spark retard and/or EGR. In comparison, pre-ignitionmay be mitigated based on the nature of the pre-ignition. In oneexample, in response to transient pre-ignition in a first cylinder,pre-ignition may be mitigated by enriching only the first cylinder whilemaintaining an engine load. If the engine is a boosted engine,pre-ignition may be further mitigated by reducing a rate of increase ofengine boost and/or throttle responsiveness. In another example, wherethe engine includes a first and a second cylinder group, the firstcylinder included in the first cylinder group, in response tosteady-state pre-ignition in the first cylinder, pre-ignition may bemitigated by enriching and load-limiting the first cylinder group andnot the second cylinder group when the pre-ignition is intermittent. Inanother example, in response to steady-state pre-ignition in the firstcylinder, pre-ignition may be mitigated by enriching and load-limitingeach of the first cylinder group and the second cylinder group when thepre-ignition is persistent. Thus, a more aggressive approach may be usedto mitigate persistent pre-ignition as compared to intermittentpre-ignition, and a more aggressive approach may be used to mitigateintermittent pre-ignition as compared to transient pre-ignition.

In this way, the same indication of pre-ignition (e.g., the same knockintensity) may be inferred as a pre-ignition event during one condition(e.g., a steady-state operating condition) but may be inferred as aknocking event during another condition (e.g., a transient operatingcondition). By adjusting the thresholds for knock and/or pre-ignitiondetection based on the rate of change of a cylinder aircharge, heavyknocking during transient conditions may be better distinguished from anactual pre-ignition event. The improved detection may allow themitigation to also be improved.

Now turning to FIG. 6, an example routine 600 is shown for adjusting apre-ignition suppressing fluid injection in response to an indication ofpre-ignition based on whether the pre-ignition occurred during transientor steady-state conditions. By varying the adjustment based on thenature of the pre-ignition, the pre-ignition mitigating effect of theinjected fluid can be improved.

At 602, engine operating conditions may be estimated and/or measured.These may include, for example, engine speed, operator torque demand,boost, exhaust temperature, etc. Further, a level of fuel available inthe fuel tanks, as well as a composition (e.g., alcohol content) of theavailable fuels (or fluids) may be determined. At 604, a rate of changeof a parameter indicative of cylinder aircharge may be determined(dAir/dt). As previously elaborated with reference to FIG. 4, based onthe rate of change being higher than a threshold, a transient engineoperating condition may be determined and a pre-ignition threshold maybe adjusted. Alternatively, based on the rate of change being lower thanthe threshold, a steady-state engine operating condition may bedetermined and a pre-ignition threshold may remain unadjusted.

At 606, it may be determined if pre-ignition has occurred. As elaboratedwith reference to FIG. 4, pre-ignition may be determined if anindication of pre-ignition (e.g., a cylinder knock intensity,ionization, in-cylinder pressure, etc.) is higher than a threshold. Thethreshold may be the adjusted or unadjusted pre-ignition threshold basedon whether the engine operating conditions are transient orsteady-state, respectively. If pre-ignition is confirmed, then at 608, acylinder (and/or engine) pre-ignition (PI) count may be determinedand/or updated. The cylinder pre-ignition count may include a trip PIcount, providing an estimate of a total number of pre-ignition events inthe cylinder over the present trip, or engine cycle, and a lifetime PIcount providing an estimate of a total number of pre-ignition events inthe cylinder over the lifetime of cylinder operation. In the same way,an engine lifetime PI count and an engine trip PI count may also beobtained. The PI count may also reflect a number of consecutivepre-ignition events in the cylinder over a specified duration (e.g.,over a number of engine cycles, a number of trips, etc.). As such, thepre-ignition count may reflect the cylinder's pre-ignition history andmay correlate with each cylinder's propensity for further pre-ignition.Thus, based on a cylinder's PI count, as well as prevalent engineoperating conditions (e.g., rate or change of cylinder aircharge), acylinder's propensity for further pre-ignition may be estimated, andused to determine how to adjust the injection profile of a pre-ignitionsuppressing fluid to the engine.

At 610, based on the determined rate of change of the cylinderaircharge, the indication of pre-ignition, and/or the cylinder PI count,the nature of the pre-ignition event may be determined. For example, inresponse to an indication of cylinder pre-ignition being higher than athreshold (e.g., an adjusted threshold), and/or a number of consecutivepre-ignition events in a cylinder (or a cylinder PI count) being higherthan a threshold, while the rate of change of the cylinder aircharge ishigher than a threshold, a transient pre-ignition condition may bedetermined. In another example, in response to an indication of cylinderpre-ignition being higher than a threshold (e.g., an unadjustedthreshold), and/or a number of consecutive pre-ignition events in acylinder (or a cylinder PI count) being higher than a threshold, whilethe rate of change of the cylinder aircharge is lower than thethreshold, a persistent steady-state pre-ignition may be determined. Incomparison, intermittent steady-state pre-ignition condition may bedetermined during steady-state conditions when the number of consecutivepre-ignition events in the cylinder (or cylinder PI count) is lower thanthe threshold.

At 612, a pre-ignition suppressing fluid injection amount to be injectedinto the pre-ignition affected cylinder may be determined. Thecontroller may first determine which fluid to inject to suppress thepre-ignition based on the fuels (or fluids) available in the fuel tanks,their fuel composition, and their fuel levels. As such, the controllermay prefer to inject a fluid having a higher water content or a highergasoline content (as compared to a higher alcohol content) due to thedilution and octane effect of water and/or gasoline, which enable ahigher pre-ignition mitigating effect. Thus in one example, if a higheramount of water is available, the controller may direct inject water tosuppress pre-ignition. In another example, if a higher amount ofgasoline is available, the controller may direct inject gasoline tosuppress pre-ignition. Further still, the controller may direct injectsome water and some gasoline. In still another example, based on thealcohol content of the available fuels, the controller may inject thefuel having the lower alcohol concentration to suppress thepre-ignition. As such, since each fluid has a different dilution effectand octane effect that contributes to pre-ignition mitigation, based onthe available fluids and their respective pre-ignition mitigatingproperties, an amount of fluid to be injected may be determined.

At 614, the profile for the pre-ignition suppressing fluid injection maybe determined based on the nature of the pre-ignition, that is, whetherthe indication of pre-ignition in the cylinder is transient,intermittent, or persistent. Specifically, the controller may adjust atiming and number of injections, in a given engine cycle, of thepre-ignition suppressing fluid injection to the pre-ignition affectedcylinder based on the nature of pre-ignition. Likewise, a split ratio ofthe pre-ignition suppressing fluid injection may also be adjusted.Herein, the split ratio refers to an amount of fluid injected earlier inan engine cycle (e.g., during an intake stroke) relative to an amountinjected later in the same engine cycle (e.g., during a compressionstroke).

At 616, a ratio of fluid (or fuel) that is direct injected into thecylinder via a direct injector relative to fluid that is port injectedinto the cylinder via a port injector is determined based on the natureof the pre-ignition. In one example, a portion of the pre-ignitionsuppressing fluid injection to be direct injected may be determined andthe remaining portion may be port injected.

In one example, based on an indication of transient pre-ignition, thenumber of injections in the given engine cycle may be increased as therate of change in the parameter indicative of cylinder airchargeincreases above the threshold. A duration between consecutive injectionsin the given engine cycle may also be based on the rate of change ofcylinder aircharge. As another example, the injection timing may beadjusted (e.g., advanced or retarded) into a transient pre-ignitionreducing injection timing, the transient pre-ignition reducing injectiontiming based on the rate of change in the parameter indicative ofcylinder aircharge and/or the PI count. As yet another example, wherethe number of injections includes at least an injection during acompression stroke of the engine and at least an injection during anintake stroke of the engine, adjusting the split ratio of the injectionin response to the indication of transient pre-ignition may includedecreasing an intake stroke injection amount relative to a compressionstroke injection amount, the split ratio based on the rate of change inthe parameter indicative of cylinder aircharge. Likewise, where aportion of the pre-ignition suppressing fluid injection is directinjected to the cylinder and a remaining portion is port injected to thecylinder, a ratio of direct injected fuel relative to port injected fuelmay be adjusted (e.g., increased) based on the rate of change in theparameter indicative of cylinder aircharge in response to the indicationof transient pre-ignition.

As such, in response to transient pre-ignition, the pre-ignitionsuppressing fluid injected may be injected only in the pre-ignitionaffected cylinder. That is, the injection may not be extended to othercylinders in the engine. Further, the adjustment may be performed for anumber of combustion events since the indication of transientpre-ignition, the number of combustion events based on the rate ofchange of the parameter indicative of cylinder aircharge. Thus, as theintensity or duration or frequency of transient pre-ignition increases,the split, multiple pre-ignition suppressing fluid injection may becontinued for a larger number of combustion events. In one example,where the injected fluid is a fuel, the injection may be a richinjection wherein a degree of the enrichment is based on the rate ofchange in the parameter indicative of cylinder aircharge (as previouslyelaborated in FIGS. 3-4).

In comparison, in response to an indication of steady-state pre-ignitionin the cylinder, the controller may adjust one or more of the timing,number of injections, and split ratio of the pre-ignition suppressingfluid injection based at least on the cylinder pre-ignition count. Forexample, the controller may increase a number of injections whiledecreasing a duration between consecutive injections in the cylinder asthe pre-ignition count of the cylinder increases above a thresholdcount. Thus, the injection profile may be adjusted to enable a moreaggressive use of the pre-ignition suppressing fluid injection duringpersistent pre-ignition as compared to intermittent pre-ignition, andlikewise during intermittent pre-ignition as compared to transientpre-ignition. As an example, in response to transient pre-ignition, thecontroller may inject a first amount of fuel over a first number ofinjections, the first number and a duration between the injections basedon the rate of change in cylinder aircharge during the transient engineoperating conditions. In another example, in response to intermittentpre-ignition, the controller may inject a second, larger amount of fuelover a second number of injections, the second number and a durationbetween the injections based on a cylinder pre-ignition count. Incomparison, in response to persistent pre-ignition, the controller mayinject a third amount of fuel over a third number of injections, thethird amount larger than each of the first and second amounts, the thirdnumber and a duration between the injections based on the cylinderpre-ignition count.

Herein, the injection in response to transient pre-ignition may becontinued for a first, smaller number of combustion events since theindication of transient pre-ignition is received, while the injection inresponse to intermittent pre-ignition is continued for a second, largernumber of combustion events since the indication of intermittentpre-ignition is received and the injection in response to persistentpre-ignition is continued for a third number of combustion events sincethe indication of persistent pre-ignition is received.

In the same way, and as elaborated with reference to FIG. 4, in responseto transient pre-ignition in a first cylinder (wherein the firstcylinder is included in a first cylinder group of the engine, and thewherein the engine further includes a second cylinder group), thecontroller may enrich only the first cylinder while maintaining anengine load. In comparison, in response to intermittent pre-ignition inthe first cylinder, the controller may enrich and limit an engine loadof the first cylinder group, while in response to persistentpre-ignition in the first cylinder, the controller may enrich and limitan engine load of each of the first and second cylinder groups. As such,the degree of enrichment and/or load-limiting responsive to persistentpre-ignition may be higher than the degree of enrichment and/orload-limiting responsive to intermittent pre-ignition, which in turn maybe higher than the degree of enrichment and/or load-limiting responsiveto transient pre-ignition.

In this way, in response to an indication of transient pre-ignition in acylinder, by direct injecting a pre-ignition suppressing fluid into thecylinder, a timing, number of injections, and split ratio of the directinjection based on a rate of change of cylinder aircharge during thetransient pre-ignition, the transient pre-ignition may be bettermitigated. By using a less aggressive pre-ignition mitigating approachin view of the presence of transient engine operating conditions, fueleconomy can be improved.

Example adjustments to a knock suppressing fluid injection profile arenow shown with reference to the example maps 700-800 of FIGS. 7-8. Ineach case, based on the nature of the pre-ignition, a pre-ignitionsuppressing fluid is injected and a timing, number of injections, andsplit ratio of the injection is adjusted.

Map 700 of FIG. 7 shows a first example wherein a number and timing ofthe injections is adjusted. Herein, in response to transientpre-ignition (PI), the number of injections may be increased to twosymmetric injections wherein each injection has the same injectionamount. Additionally, a duration between consecutive injections may beadjusted (e.g., increased) such that the average injection timing is atthe same timing as a corresponding single injection of the total amountof fluid. In response to intermittent pre-ignition, the number ofinjections may also be increased to two symmetric injections whereineach injection has the same injection amount. Herein, due to theintermittent nature of the pre-ignition, a duration between consecutiveinjections may be adjusted (e.g., decreased relative to transientpre-ignition) such that the average injection timing is at the sametiming as a corresponding single injection of the total amount of fluid.Additionally, the average injection timing for the injection responsiveto intermittent pre-ignition may be retarded relative to the averageinjection timing for the injection responsive to transient pre-ignition.In comparison, in response to persistent PI, the number of injectionsmay be further increased (herein, to three symmetric injections) whereineach injection has the same injection amount. Further, due to thepersistent nature of the pre-ignition, a duration between consecutiveinjections may be adjusted (e.g., further decreased relative totransient and intermittent pre-ignition) such that the average injectiontiming is at the same timing as a corresponding single injection of thetotal amount of fluid. Additionally, the average injection timing forthe injection responsive to persistent pre-ignition may be retardedrelative to the average injection timing for the injection responsive totransient pre-ignition as well as intermittent pre-ignition.

It will be appreciated that while the depicted example illustrates splitsymmetric injections, in alternate embodiments, the different injectionsmay be asymmetric with the first injection amount differing fromconsecutive injection amounts. In one example, a smaller portion of thetotal injection amount may be injected in the first split injection tomitigate transient pre-ignition while a larger portion of the totalinjection amount may be injected in later injections of the splitinjection to mitigate intermittent or persistent pre-ignition (with thelatter portion being higher for persistent as compared to intermittentpre-ignition). It will also be appreciated that while the depictedexample illustrates the split injections being injected in the samestroke of an engine cycle, in still other embodiments, the splitinjections may be injected in a combination of different strokes of agiven engine cycle.

One such example is shown in FIG. 8. Map 800 of FIG. 8 shows a firstexample wherein in response to transient pre-ignition (PI), the numberof injections of a pre-ignition suppressing fluid injection isincreased, herein to two asymmetric injections wherein the firstinjection has a higher injection amount than the second injection.Additionally, the two injections are performed within an intake strokeof the engine cycle. In comparison, in response to intermittentpre-ignition, the number of injections is increased, herein also to twoasymmetric injections, with the first injection having a smallerinjection amount than the second injection. Herein, in addition todecreasing a duration between consecutive injections and retarding anaverage injection timing relative to the transient pre-ignition timing,the split ratio of the injection is adjusted such that a smaller portionof the injected fluid is injected earlier in a given engine cycle(herein, in the intake stroke) while the remaining larger portion of theinjected fluid is injected later in the engine cycle (e.g., in acompression stroke) to mitigate pre-ignition. As another example, inresponse to persistent pre-ignition, the number of injections is furtherincreased, herein to three asymmetric injections, with the thirdinjection having a higher injection amount than each of the first andsecond injections. Further, in addition to decreasing a duration betweenconsecutive injections and retarding an average injection timingrelative to the transient and intermittent pre-ignition timing, thesplit ratio of the injection is adjusted such that a further smallerportion of the injected fluid is injected earlier in the given enginecycle (herein, in the intake stroke) while the remaining larger portionof the injected fluid is injected later in the engine cycle (e.g., in acompression stroke) to mitigate pre-ignition. While the depicted exampleillustrates the injection amount being split between an intake strokeand a compression stroke, still other combinations may be possible.

In this way, the detection of transient pre-ignition and differentiationfrom intermittent and persistent pre-ignition can be improved. Also, byadjusting the pre-ignition mitigating action (e.g., enrichment,load-limiting and/or injection of a pre-ignition suppressing fluid)based on the nature of the pre-ignition, the pre-ignition mitigatingeffect can be improved and further pre-ignition can be reduced. Byreducing erroneous pre-ignition detection during transient conditions,fuel wastage and degraded exhaust emissions due to unnecessary cylinderenrichment can be reduced. In this way, engine fuel economy and exhaustemissions can also be improved.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The specific routines described herein may represent one or more of anynumber of processing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various acts,operations, or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example embodiments described herein, but is providedfor ease of illustration and description. One or more of the illustratedacts or functions may be repeatedly performed depending on theparticular strategy being used. Further, the described acts maygraphically represent code to be programmed into the computer readablestorage medium in the engine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

1. A method for an engine, comprising: adjusting a timing and number ofinjections, in a given engine cycle, of a pre-ignition suppressing fluidinjection to a cylinder based on an indication of transient pre-ignitionin the cylinder.
 2. The method of claim 1, further comprising, adjustinga split ratio of the pre-ignition suppressing fluid injection based onthe indication of transient pre-ignition.
 3. The method of claim 2,wherein the indication of transient pre-ignition in the cylinderincludes an indication of pre-ignition being higher than a thresholdwhile a rate of change in a parameter indicative of cylinder airchargeis higher than a threshold rate.
 4. The method of claim 3, whereinadjusting the number of injections includes increasing the number ofinjections in the given engine cycle as the rate of change in theparameter indicative of cylinder aircharge increases above thethreshold.
 5. The method of claim 4, wherein a duration betweenconsecutive injections in the given engine cycle is based on the rate ofchange in the parameter indicative of cylinder aircharge.
 6. The methodof claim 5, wherein adjusting the timing includes adjusting the timinginto a transient pre-ignition reducing injection timing, the transientpre-ignition reducing injection timing based on the rate of change inthe parameter indicative of cylinder aircharge.
 7. The method of claim6, wherein the knock-suppressing fluid includes one or more of water,ethanol, and gasoline.
 8. The method of claim 7, wherein the number ofinjections includes at least an injection during a compression stroke ofthe engine and at least an injection during an intake stroke of theengine, and wherein adjusting the split ratio includes decreasing anintake stroke injection amount relative to a compression strokeinjection amount in response to the indication of transientpre-ignition, the split ratio based on the rate of change in theparameter indicative of cylinder aircharge.
 9. The method of claim 8,wherein a portion of the pre-ignition suppressing fluid injection isdirect injected to the cylinder and a remaining portion is port injectedto the cylinder, a ratio of direct injected fuel relative to portinjected fuel based on the rate of change in the parameter indicative ofcylinder aircharge.
 10. The method of claim 3, wherein the indication ofpre-ignition includes on one or more of a knock sensor output, acrankshaft acceleration, an ionization sensor output, and an in-cylinderpressure, and wherein the parameter indicative of cylinder airchargeincludes one or more of manifold air pressure, manifold air flow,cylinder aircharge, and a throttle position.
 11. The method of claim 3,wherein the adjustment is performed for a number of combustion eventssince the indication of transient pre-ignition, the number of combustionevents based on the rate of change of the parameter indicative ofcylinder aircharge.
 12. The method of claim 3, wherein a degree ofenrichment of the pre-ignition suppressing fluid injection is based onthe rate of change in the parameter indicative of cylinder aircharge.13. The method of claim 3, wherein the pre-ignition suppressing fluid isinjected only in the pre-ignition affected cylinder.
 14. The method ofclaim 13, further comprising, in response to an indication ofsteady-state pre-ignition in the cylinder, adjusting one or more of thetiming, number of injections, and split ratio of the pre-ignitionsuppressing fluid injection based on a cylinder pre-ignition count, theindication of steady state pre-ignition including an indication ofpre-ignition being higher than a threshold while the rate of change in aparameter indicative of cylinder aircharge is lower than the thresholdrate, the indication including, increasing a number of injections whiledecreasing a duration between consecutive injections in the cylinder asthe pre-ignition count of the cylinder increases above a thresholdcount.
 15. A method for an engine cylinder, comprising: in response totransient pre-ignition, injecting a first amount of fuel over a firstnumber of injections, the first number and a duration between theinjections based on rate of change in cylinder aircharge; in response tointermittent pre-ignition, injecting a second, larger amount of fuelover a second number of injections, the second number and a durationbetween the injections based on a cylinder pre-ignition count; and inresponse to persistent pre-ignition, injecting a third amount of fuelover a third number of injections, the third amount larger than each ofthe first and second amounts, the third number and a duration betweenthe injections based on the cylinder pre-ignition count.
 16. The methodof claim 15, wherein the injection in response to transient pre-ignitionis continued for a first, smaller number of combustion events since anindication of transient pre-ignition, wherein the injection in responseto intermittent pre-ignition is continued for a second, larger number ofcombustion events since an indication of intermittent pre-ignition, andwherein the injection in response to persistent pre-ignition iscontinued for a third number of combustion events since an indication ofpersistent pre-ignition.
 17. The method of claim 16, wherein thecylinder is a first cylinder in a first cylinder group, the enginefurther including a second cylinder group, the method furthercomprising: in response to transient pre-ignition in the first cylinder,enriching only the first cylinder while maintaining an engine load; inresponse to intermittent pre-ignition in the first cylinder, enrichingand limiting an engine load of the first cylinder group; and in responseto persistent pre-ignition in the first cylinder, enriching and limitingan engine load of each of the first and second cylinder group.
 18. Themethod of claim 17, wherein the intermittent pre-ignition includes anumber of consecutive pre-ignition events in the first cylinder beinglower than a threshold while the engine is in a steady-state, whereinthe persistent pre-ignition includes a number of consecutivepre-ignition events in the first cylinder being higher than thethreshold while the engine is in the steady-state, and wherein thetransient pre-ignition includes a number of consecutive pre-ignitionevents in the first cylinder being higher than the threshold while theengine is in a transient state.
 19. The method of claim 18, wherein thesteady-state includes a rate of change of a parameter indicative ofcylinder aircharge being lower than a threshold, and wherein thetransient state includes a rate of change of a parameter indicative ofcylinder aircharge being higher than a threshold.
 20. A method for anengine, comprising: in response to an indication of transientpre-ignition in a cylinder, direct injecting one or more of water,ethanol, and gasoline into the cylinder, a timing, number of injections,and split ratio of the direct injection based on a rate of change ofcylinder aircharge during the transient pre-ignition.